Gas water heater with increased thermal efficiency and safety

ABSTRACT

A gas water heater having increased thermal efficiency comprises a water tank having a sealed combustion chamber thereunder. An atmospheric burner is located in the combustion chamber. A flue pipe extends from the sealed combustion chamber and through the water tank for heat exchange of hot atmospheric gas therein with water in the water tank. A heat exchanger is in communication with the combustion gases exiting the water tank to extract residual heat from the combustion gas in the flue pipe for mixture with ambient air to produce pre-heated combustion air. An air convection or draft inducing device directs the hot combustion air from the heat exchanger through a sealed conduit to direct the pre-heated combustion air to the combustion chamber.

TECHNICAL FIELD

The present invention relates to a gas water heater having increasedthermal efficiency and wherein pre-heated combustion air is drawn fromabove the water heater housing.

BACKGROUND OF THE ART

It is known from our pending application Ser. No. 12/886,910 filed Sep.21, 2010 to provide heat exchangers with hot water heaters whereby toextract residual heat from the flue gases exiting the water heater toheat ambient air in the surrounding space and/or to feed the recoveredheat into the ducting system of the building.

It is also known in the prior art to integrate heat pumps with domestichot water heaters wherein the hot gases are used in heat exchange withwater circulated from the hot water heater to provide an added heatsource to heat water and this usually results in complex devicesintegrated together in a single unit. A disadvantage of these integratedsystems is that they are expensive to fabricate and require additionalmaintenance. Also, after the life cycle of the water tank it isnecessary to also discard the integrated heat exchange devices.Accordingly, such hot water heaters are expensive to fabricate andmaintain and the economical advantages of such systems are therefore notrealizable due to added costs.

Explosion proof water heaters are also known wherein combustion air isdrawn through a pipe which is elevated from the floor and wherein thecombustion chamber is sealed whereby explosive gases, which are denserthan air, will not enter the combustion chamber through the bottom endof the water heater and cause an explosion. However, these combustionair conduits have been known to block due to debris such as lintentering the conduit or blocking a screen at the entrance. Children mayalso find it convenient to introduce objects in the screen opening. Itis also known to provide gas detectors on the exterior wall of the waterheater and close to the bottom end thereof whereby to detect able vaporsand upon detection to shut off the gas supply to the water heater.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide a gas water heaterhaving increased thermal efficiency and which substantially overcomesthe above disadvantages of the prior art.

According to a further feature of the present invention there isprovided a gas water heater having increased thermal efficiency andwherein the combustion air is pre-heated prior to being introduced inthe combustion chamber by heat extracted from the residual gases exitingthe water heater through the flue pipe.

Another feature of the present invention is to draw the combustion airabove the water heater and feed it to the bottom combustion chamber in aprotected duct and with the combustion air being heated by residual heatfrom the flue pipe above the water heater.

Another feature of the present invention is to provide a gas waterheater having increased thermal efficiency and having a sealedcombustion chamber with a gas detector located externally of the waterheater to detect explosive gases in the vicinity of the water heater toshut off the water heater thereby preventing explosion.

According to the above features, from a broad aspect, the presentinvention provides a gas water heater having increased thermalefficiency and which is comprised of a water tank having a sealedcombustion chamber thereunder. An atmospheric burner is provided in thesealed combustion chamber. A flue pipe extends from the sealedcombustion chamber and through the water tank for heat exchange of hotcombustion gas therein with water in the water tank. A heat exchanger isin communication with the combustion gases exiting the water tank toextract residual heat from the combustion gas for mixture with ambientair to produce heated combustion air. A draft inducing means is providedto pull the hot combustion gases from the combustion chamber through theflue pipe. Conduit means is also provided to direct the pre-heatedcombustion air to the combustion chamber.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a gas water heater constructed inaccordance with the present invention and provided with a heat exchangerin a top of the hot water heater and a conduit extending from the heatexchanger to the sealed combustion chamber at the bottom of the gaswater heater to supply pre-heated combustion air to the combustionchamber; and

FIG. 2 is a fragmented view showing the construction of the gas waterheater of the present invention as shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, there is shown generally at 10 a gaswater heater constructed in accordance with the present invention. Asbetter seen in FIG. 2 the gas water heater has a water tank which is aglass lined steel tank 11 for containing water to be heated. Cold wateris admitted inside the water tank through a diptube 12 connected to acold water inlet, herein the pressurized domestic cold water supply 13.Such supplies are equipped with a shut-off valve 14. Hot water isextracted from the tank 11 from the top end thereof through a hot waterline 15, also provided with a shut-off valve 16.

In the particular embodiment of the gas water heater of the presentinvention a sealed combustion chamber 17 is provided under the innertank 11 and is provided with an atmospheric gas burner 18. An outercasing 19 is provided secured spaced around the inner tank 11 and athermal insulation, not shown, is introduced in the gap 24 between theouter casing 19 and the inner tank 11. The gas supply to the burner 18is provided through a gas control device 20. The gas conduit 21 as wellas the temperature sensor 22 and ignition unit 23 are introduced intothe combustion chamber and hot water tank through sealed gaskets, notshown therein, but obvious to a person skilled in the art.

As shown in FIG. 2 hot combustion gases from the atmospheric burner exitthe combustion chamber through a flue pipe 25. A baffle plate assembly26 is mounted within the flue pipe to slow down the hot flue gases forbetter heat exchange of the hot flue gases with the water surrounding itcontained within the water tank 11. A blower unit 27 draws the hotcombustion gases through the flue pipe 25. A draft inducing means suchas a small fan can replace the blower 27.

As herein shown the hot water heater of the present invention isprovided with a heat exchanger 30 mounted at a top end thereof and incommunication with the exit end 31 of the flue pipe exiting the top wall32 of the outer casing 19 surrounding the inner hot water tank 11. Theheat exchanger 30 is provided with a plurality of spaced-apart conduits33 mounted in a heat exchange assembly comprised of a plurality of heatsink plates 34 for extracting heat rising in the conduits 33 from abottom chamber 35 of the heat exchanger and exiting into an upperchamber 36 which is connected to the venting conduit 37 leading to theoutside of a building containing the hot water heater whereby to releasethe cooled flue gases into the atmosphere. The heat exchanger 30 isherein contained within a heat exchanger housing 40 which has a portionof its sidewall 41 perforated, such as shown at 42, to provide for theadmission of ambient air therein. The ambient air inside the heatexchanger housing 40 is heated by the heat exchanger 30 and drawn orpushed into a sealed conduit 45, which is better illustrated in FIG. 1,and which is in sealing contact about the outer surface 19′ of the outercasing 19.

The sealed conduit 45 draws air above the water heater and its inlet 48is protected by the housing 40. The heated air is drawn into the sealedconduit 45 which at its lower end is secured to an air inlet port 47 ofthe sealed combustion chamber 17. The hot air from the heat exchangerhousing 40 is drawn in to the sealed conduit 45 by the draft created bythe blower unit 27 which draws air from the flue pipe and from thesealed combustion chamber thereby causing a suction in the sealedconduit 45 to create a combustion air flow. Optionally, a combustion airfan 47 may be secured at the inlet 48 of the sealed combustion conduitto create a stronger air flow through the heat exchanger housing 40.Accordingly, the air displacement means through the sealed conduit canbe realised by the blower unit 27 assisted by an air combustion fan 47.The blower unit 27 may also not be necessary and the fan 47 may besufficient to create the draft in the flue pipe together with the hotrising combustion gases. One advantage of this unit is that it can use adraft inducer instead of the blower 27 so that the pressure in the ventsystem could remain non-positive thus fall into Category II applianceand be vented with Category II chimney (non-positive vent staticpressure—condensing). One could also use a blower and fall into CategoryIV appliance and be vented with Category IV chimney (positive ventstatic pressure—condensing).

As herein shown and described, the heat exchanger 30 an air-to-air heatexchanger fabricated from a plurality of conduits and heat sink plates,but other form of heat exchangers may be used to extract the residualheat from the flue gases and used for heating combustion air for feedingthe sealed combustion chamber through the conduit 45. As also hereinshown a condensate drain pipe 49 is secured to the heat exchanger 30 toevacuate condensate therefrom as the hot flue gases are cooled by theextraction of heat therefrom. Further, because the flue gases have beenconsiderably cooled by the combination of the baffle 26 and the heatexchanger 30 the flue gases exiting the heat exchanger 30 are cooledenough to use venting conduits 37 constructed from plastic materials,such as PVC plastic piping.

Because the gas water heater of the present invention uses a sealedcombustion chamber with increased thermal efficiency due to thepre-heating of combustion air and further seeing because the combustionair is taken from above the hot water heater in a protective heatexchanger housing, the combustion air flow path is from the top of thewater heater down into a sealed conduit extending vertically along thesidewall of the outer casing of the water heater and into the sealedcombustion chamber at the bottom thereof. Accordingly, the hot waterheater is substantially sealed all along its height leading to the topheat exchanger housing 40. Therefore, any explosive gas that may leak onthe floor in the lower end of the hot water heater will not enter intothe combustion chamber to cause an explosion. However, to provide addedsecurity there may be provided a gas detector 50 mounted exteriorly at alower end of the outer casing 19 to detect explosive gases close to thebottom end of the hot water heater and provide an alarm conditioncausing the gas control device 20 to shut off the gas supply to theburner and provide an alarm indicating that such gases have beendetected and that remedial action is necessary. An added safety featureis provided by having the combustion air inlet located higher from thefloor above the water heater tank in a protective housing to preventeasy access thereto.

It is within the ambit of the present invention to cover any obviousmodifications of the preferred embodiment described herein provided suchmodifications fall within the scope of the appended claims,

1. A gas water heater having increased thermal efficiency comprising awater tank having a sealed combustion chamber thereunder, an atmosphericburner in said sealed combustion chamber, a flue pipe extending fromsaid sealed combustion chamber and through said water tank for heatexchange of hot combustion gas therein with water in said water tank, aheat exchanger in communication with said combustion gases exiting saidwater tank to extract residual heat from said combustion gas for mixturewith ambient air to produce pre-heated combustion air, draft inducingmeans to pull said hot combustion gases from said combustion chamberthrough said flue pipe, and conduit means to direct said pre-heatedcombustion air to said combustion chamber.
 2. A gas water heater asclaimed in claim I, wherein said conduit means is a sealed conduit, andair displacement means to displace said pre-heated combustion air into atop end of said sealed conduit and therethrough; said sealed conduitcommunicating, at a lower end thereof, with a combustion air inlet portof said sealed combustion chamber.
 3. A gas water heater as claimed inclaim 2, wherein said displacement means is a fan.
 4. A gas water heateras claimed in claim 1, wherein said flue pipe is provided h bafflestherein to slow said hot flue gases therein for heating said flue pipein heat exchange with water in said water tank.
 5. A gas water heater asclaimed in claim wherein said heat exchanger is an air-to-air heatexchanger.
 6. A gas water heater as claimed in claim 1, wherein there isfurther provided condensate evacuation means to evacuate condensate fromsaid heat exchanger.
 7. A gas water heater as claimed in claim 1,wherein said flue pipe above said heat exchanger is a plastic vent pipeadequate to exhaust cooled combustion gases from an outlet of said heatexchanger.
 8. A gas water heater as claimed in claim 1, wherein saiddraft inducing means creates a combustion air flow path from a top endof said gas water heater. where combustion air is extracted andpre-heated, to be sealingly directed to said sealed combustion chamberand exhausted to atmosphere after heat extraction therefrom, said gaswater heater having a gas detector exteriorly mounted at a lower endthereof to detect explosive gases to provide for an explosion proof gaswater heater.
 9. A gas water heater as claimed in claim 2, wherein saidconduit means is a combustion air conduit sealingly secured to an outercasing of said hot water heater, said water tank being a glass linedsteel tank, thermal insulation between said steel tank and said outercasing, said heat exchanger being secured in a heat exchanger housingsecured above a top end of said outer casing, said heat exchangerhousing having air inlet means, and a fan in said heat exchanger housingconstituting said air displacement means to draw in ambient air intosaid heat exchanger and direct it in a top end of said combustion airconduit where it is connected to said combustion chamber for admixturewith combustible fuel fed to said atmospheric burner.
 10. A gas waterheater as claimed in claim 2, wherein said top end of said sealedconduit is surrounded by a protective housing secured above said gaswater heater water tank. A gas water heater as claimed in claim 10,wherein said protective housing is a housing surrounding said heatexchanger.